1. Field of the Invention
The present invention relates to a method for inspecting a settling time of a deflection amplifier, and a method for judging a failure of a deflection amplifier. For example, it relates to a method for inspecting a settling time of a shaping amplifier for deflecting electron beams, which is installed in an electron beam writing apparatus that deflects variable-shaped electron beams to irradiate a target workpiece, and to a method for detecting a failure of a shaping amplifier.
2. Description of Related Art
The microlithography technique which advances micro-miniaturization of semiconductor devices is extremely important as being the only process of forming patterns in semiconductor manufacturing processes. In recent years, with high integration of large-scale integrated circuits (LSI), critical dimensions required for semiconductor device circuits are shrinking year by year. In order to form a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is required. Then, the electron beam writing technique intrinsically having excellent resolution is used for producing such highly precise master patterns.
FIG. 13 is a schematic diagram showing operations of a conventional variable-shaped electron beam (EB) type writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus, including two aperture plates, operates as follows: A first aperture plate 410 has a quadrangular such as rectangular opening or “hole” 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that passed through the opening 411 into a desired rectangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shaped opening 421 and thereby to irradiate a target workpiece or “sample” 340 mounted on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing or “drawing.” In other words, a rectangular shaped as a result of passing through both the opening 411 and the variable-shaped opening 421 is written in the writing region of the target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a “variable shaped” method.
In the pattern writing apparatus, as mentioned above, a pattern is projected onto a target workpiece by a deflection of a charged particle beam, such as an electron beam. A deflection amplifier is used for such a beam deflection. As functions of the beam deflection using the deflection amplifier, controlling the shape or size of an electron beam being shot, controlling a shot position, and blanking the beam can be exemplified.
In recent years, a throughput requested for the electron beam pattern writing apparatus is very high. Then, it is also requested to shorten a preparation time (settling time) with respect to a shot position or a beam shaping. Although the settling time can be set arbitrarily, if it is set long, the throughput is lowered by that much. Conversely, if the settling time is too short, since sufficient voltage is not applied to a deflector, necessary deflection is not performed. Consequently, an error may occur with respect to a pattern dimension or a shot position. Therefore, finding the optimal settling time is needed. Conventionally, in order to find the optimal settling time, writing onto a substrate on which resist is applied, developing the written substrate, and measuring the dimension of a pattern formed by etching are actually performed. Then, repeatedly performing these operations while changing the settling time, a settling time based on which a highly precise pattern dimension has been shaped is regarded as the optimal settling time. These operations need about ten hours conventionally, and thereby reducing the time for operations is requested.
Moreover, when an error occurs with respect to a pattern dimension or a shot position, identifying the cause of the error becomes necessary. If it is possible to quickly judge whether the cause is a failure of a shaping amplifier or not, the down-time period of the apparatus can be shortened. Therefore, a method for quickly judging a failure of a shaping amplifier is requested. Then, as a cause of a failure of the shaping amplifier, degradation of the settling performance occupies much of the cause. Therefore, a method for quickly judging whether the settling performance has deteriorated or not is requested. However, a sufficient judgment method has not been conventionally established.
Although not related to a defect of the shaping amplifier, a technique is disclosed that inputs deflection data into one of two shaping amplifiers and time differentially inputs another deflection data, having a direction reverse to the former one, into the other shaping amplifier at a certain cycle before and after writing, and measures a voltage change at the middle point of a measurement resistance between respective outputs by using an oscilloscope in order to detect the settling time of the shaping amplifier (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2004-259812).
As mentioned above, a method for quickly finding the optimal settling time is requested, and a method for quickly judging whether the settling performance has deteriorated or not is also requested. However, no sufficient methods have been established.